From: Xuewen Yan <xuewen.yan94@gmail.com>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Quentin Perret <qperret@google.com>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Steven Rostedt <rostedt@goodmis.org>,
Benjamin Segall <bsegall@google.com>,
Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
quentin.perret@arm.com, Chunyan Zhang <zhang.lyra@gmail.com>,
Ryan Y <xuewyan@foxmail.com>,
Pierre Gondois <pierre.gondois@arm.com>
Subject: Re: [PATCH] sched/fair: use signed long when compute energy delta in eas
Date: Tue, 6 Apr 2021 18:59:16 +0800 [thread overview]
Message-ID: <CAB8ipk9JATYxJBnpVFfH_XHLqh=yHesbo73wx=Mm7t8mSqW_Gg@mail.gmail.com> (raw)
In-Reply-To: <34ce11ad-9c20-7ba7-90d8-4830725bf38a@arm.com>
Hi Dietmar
On Fri, Apr 2, 2021 at 2:07 AM Dietmar Eggemann
<dietmar.eggemann@arm.com> wrote:
>
> +cc: Pierre Gondois <pierre.gondois@arm.com>
>
> On 30/03/2021 11:45, Quentin Perret wrote:
> > Hi,
> >
> > On Tuesday 30 Mar 2021 at 13:21:54 (+0800), Xuewen Yan wrote:
> >> From: Xuewen Yan <xuewen.yan@unisoc.com>
> >>
> >> now the energy delta compute as follow:
> >>
> >> base_energy_pd = compute_energy(p, -1, pd);
> >> --->Traverse all CPUs in pd
> >> --->em_pd_energy()
> >> ----------------------------------------------------- \
> >> search for the max_sapre_cap_cpu \
> >> --------------------------------- search time
> >> cur_delta = compute_energy(p, max_spare_cap_cpu, pd); /
> >> --->Traverse all CPUs in pd /
> >> ---------------------------------------------------- /
> >> --->em_pd_energy()
> >> cur_delta -= base_energy_pd;
> >>
> >> During the search_time, or when calculate the cpu_util in
> >> compute_energy(), there may occurred task dequeue or cpu_util change,
> >> it may cause the cur_energy < base_energy_pd, so the cur_delta
> >> would be negative. But the cur_delta is unsigned long, at this time,
> >> the cur_delta would always bigger than best_delta of last pd.
> >>
> >> Change the vars to signed long.
> >
> > Is that really helping though?
> >
> > Yes you will not overflow, but the decision is still 'wrong' if the util
> > values are not stable for the entire wake-up. I think folks on the Arm
> > side had patches to try and cache the util values upfront, and then use
> > them throughout feec() and compute_energy(), which I think would be a
> > better fix.
> >
> > Dietmar, wdyt?
>
> Yes, we have some patches from Pierre Gondois which introduce a pd cache
> to store the CPU utilization values so they can be reused for 'cpu !=
> dst_cpu' calculations within find_energy_efficient_cpu() (feec()).
>
> We did run them in our Jan 2021 EAS integration:
>
> https://gitlab.arm.com/linux-arm/linux-power/-/commits/eas/next/integration-20210129
>
> sched: Allocate pd_cache when EAS is enabled
> sched/fair: Use pd_cache to speed up find_energy_efficient_cpu()
>
> We haven't posted them since we're still looking for a story to justify
> the extra complexity. The experiments on Arm64 Juno (2 big, 4 little
> CPUs) showed 1-2% failure due to changes of CPU utilization values
> during feec(). There was a 5% (big CPU)-10% (little CPU) runtime
> reduction for feec() with the patches.
I test the patch, but the overflow still exists.
In the "sched/fair: Use pd_cache to speed up find_energy_efficient_cpu()"
I wonder why recompute the cpu util when cpu==dst_cpu in compute_energy(),
when the dst_cpu's util change, it also would cause the overflow.
Thanks
next prev parent reply other threads:[~2021-04-06 11:00 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-30 5:21 [PATCH] sched/fair: use signed long when compute energy delta in eas Xuewen Yan
2021-03-30 9:45 ` Quentin Perret
2021-04-01 18:07 ` Dietmar Eggemann
2021-04-06 10:59 ` Xuewen Yan [this message]
2021-04-07 14:11 ` Pierre
2021-04-08 5:41 ` Xuewen Yan
2021-04-08 9:33 ` Pierre
2021-04-09 2:20 ` Xuewen Yan
2021-04-12 10:26 ` Pierre Gondois
2021-04-12 10:52 ` Xuewen Yan
2021-04-12 17:14 ` Pierre Gondois
2021-04-13 1:50 ` Xuewen Yan
2021-04-13 10:58 ` Pierre Gondois
2021-04-13 11:59 ` Xuewen Yan
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